Inductive charging (also referred to as “wireless charging”) uses a magnetic field to transfer energy between two objects. Energy is transmitted from a charging station to a portable electrical device, for example, using inductive coupling. Within the portable device the magnetic field-induced electrical current can charge batteries or supply power to operate the portable device.
Inductive chargers typically comprise a charging induction coil for creating a time-changing magnetic field within the charging station. The portable device comprises a receiving induction coil magnetically coupled to the charging induction coil. The proximate charging and receiving induction coils cooperate to form an electrical transformer and thus the time-changing magnetic field produced by the charging induction coil generates a current in the receiving induction coil. Thus the magnetic field transfers energy from the charging coil to the receiving coil for powering the portable device or for charging a battery in the portable device. Each of the charging and receiving coils typically comprise a plurality of coils that are referred to herein as a coil array.
One disadvantage of inductive charging is the relatively low power transfer efficiency and increased resistive heating when compared to direct contact (wired) current charging. This efficiency problem is exacerbated when one or both of the charging coil array and the receiving coil array moves relative to the other. Despite its disadvantages, inductive charging may be required in certain applications where wired contact is not desired, such as for charging batteries in an electrical device that cannot be directly connected to the charging station or an electrical device that is portable or moveable relative to the charging station.